Replace forEach with for-of loops in generateExterns
Replace forEach with for-of loops in generateExterns

Issue #1157

Change-Id: I6590827b82f459a926536b916a2d2e01a89135ed

tvoli/shaka-player,tvoli/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player